LTE Q&A

 1. What is central frequency, DC frequency? How is it transmitted from eNB and how UE detects it?

2. PCI = 3SSS+PSS why is this way?

Important Transport layer ports

20 - First - FTP - File Transfer Protocol - Data 

21 - First - FTP Control messages

FTP is exclusive to TCP, since connection should be established before Data getting transmitted.

22 - Second - SSH -Secure Shell

SSH can run on both TCP and UDP. TCP is default setting.

23 - Third - Telnet

Telnet strictly uses TCP, it cannot be used on UDP.

25 - SMTP - Simple Main Transfer Protocol

53 - DNS - Domain Name server

DNS works on UDP

67 - DHCP Server

68 - DHCP Client

DHCP works on UDP, Since there is a broadcast on server reply it is required to use 2 ports separately for client and server to differentiate origin of message.

80 - HTTP - Hyper Text Transfer Protocol

443 - HTTPS - Hyper Text Transfer Protocol Secured

HTTP generally runs on TCP, however it can be implemented on UDP as well.

161 - SNMP Agents

162 - SNMP Traps

SNMP uses UDP

520 - RIP - Routing Information Protocol

RIP uses UDP on transport layer

143 - IMAP - Internet Message Access Protocol

GIT - VCS 

Git is a Distributed version control system.

 

Why distributed

We can write the code offline and update whenever we become online. We need not be online while writing code.

Also, we can import from the respository the whole version from anywhere and work on it.

 

Features of Git

We can branch out from a ongoing version and work on specific feature, then merge the code with main version.

 

Ways of Git working

a.       Working from a local repository

a.     

Commands

At remote/cloud, copy the clone URL and at git bash clone it to sync with remote directory.

$ git clone <URL>

At local git bash

When you are ready with working copy, we need to add the copy to staging area.

Staging area is like draft area, we can add one or multiple files to be committed in staging area

a.       $ git add

 

After adding to staging area, code should be pushed to local repository by using “git commit” comment. After committing, code will have a version in local repository. Also we are required to add a comment for the version we are committing

b.       $ git commit -m <message>

After commit, we must push the copy to remote/cloud repository. This would be done only if remote repository is cloned before starting the process from step a. above.

c.       $ git push

 

 

When remote repository is not cloned or To add a new repo to from local or existing to remote repo, use following

When creating new working directory

1.           $ git init

2.       $ git add README.md

3.       $ git commit -m <message>

4.       $ git remote add origin <git repo url>

5.       $ git push -u origin master

 

When using existing/non version local code to remote repo

1.       $ git remote add origin <git repo url>

2.       $ git push -u origin master

Sometime you get error like below when you push code, this is because sometimes the branch pointing at remote repo is different from local.

“

$ git push https://github.com/ramvdy/Localfootprint.git

To https://github.com/ramvdy/Localfootprint.git

 ! [rejected]        main -> main (non-fast-forward)

error: failed to push some refs to 'https://github.com/ramvdy/Localfootprint.git'

hint: Updates were rejected because the tip of your current branch is behind

hint: its remote counterpart. Integrate the remote changes (e.g.

hint: 'git pull ...') before pushing again.

hint: See the 'Note about fast-forwards' in 'git push --help' for details.

”

When we face this we need to use “git pull” command to integrate. This basically merges the code, under remote branch

So command “git pull --rebase” would put your version on top and remote under your branch.

When things fail as shown in above error capture, need to try git pull and then pushed

 

Push command after the pull is successful is

$ git push --set-upstream origin main

 

Detailed write up on how git pull merge fetch and rebase works below.

""""

383

From your feature branch (e.g configUpdate) run:

git fetch

git rebase origin/master

Or the shorter form:

git pull --rebase

---

Why this works:

·         git merge branchname takes new commits from the branch branchname, and adds them to the current branch. If necessary, it automatically adds a "Merge" commit on top.

·         git rebase branchname takes new commits from the branch branchname, and inserts them "under" your changes. More precisely, it modifies the history of the current branch such that it is based on the tip of branchname, with any changes you made on top of that.

·         git pull is basically the same as git fetch; git merge origin/master.

·         git pull --rebase is basically the same as git fetch; git rebase origin/master.

So why would you want to use git pull --rebase rather than git pull? Here's a simple example:

·         You start working on a new feature.

·         By the time you're ready to push your changes, several commits have been pushed by other developers.

·         If you git pull (which uses merge), your changes will be buried by the new commits, in addition to an automatically-created merge commit.

·         If you git pull --rebase instead, git will fast forward your master to upstream's, then apply your changes on top.

 """"

 

5 Things To Know About Telecom Network

Telecom Network is the one which everyone uses these days, yet not many people know what it is exactly behind the scenes. Many of us have familiar with famous Gs like 2G, 3G, here G represents generation. 2G stands for 2nd generation, 3G for 3rd generation and so on.

1. Gs at network level
When they say 2G, 3G, 4G and 5G, these mainly represent the features of radio network. The backbone network is not called with Gs. However backbone network also changes with each generation of radio network. There is a international body ITU-T which sets the guidelines for upcoming generation. If a given technology meets the criteria then it is qualified to be G of that period.

2. G doesn't mean all network
As each generation (Gs) progress, backbone network also evolves accordingly, however it is not necessarily happen at the same time. Backbone network evolution might take different timeline.
When we say evolution, it means supporting the speed, features with each generation of network offers.

3.
Many might get wondered by the fact that, Mobile network is wireless only till the base station. From the base station, all call and data will be processed on wired/optical network. When a person calls from a cell phone, signals travels to base station via wireless radio network, then base station carries signal over copper cables or optical fiber to switching systems. Switching systems will determine the where call has to be routed to reach the destination user.

4. On the switching network side there will be mainly 2 sub networks, one will cater voice services another will cater internet services. Voice network has altogether different architecture than internet network. This gap is narrowing down now, as most of the services are provided over internet services. Within voice network  there is TDM (Time Division Multiplexing) network and IP network, voice calls could travel through both these networks when you make call.

5. You might be wondered which generation the landline phones belong to. This is a slightly different story, as landlines are not so popular now, there is no rapid changes in this sector. Yet we have a evolution in landlines, which is as follows
      a. POTS (Plain Old Telephony Services) also called PSTN (Public Switched Telephony Network), this offers only voice services.
      b. ISDN (Integrated Services Digital Network), this network offers integrated Voice, Video and Internet services on a subscriber line. Voice and Video conferencing was the major service offered on this network.
      c. VOIP (Voice Over Internet Protocol), VOIP network offers caters wide range of services. VOIP operates on internet protocol which makes it flexible to implement. Through VOIP, it becomes easier to connect. One of the major advantage of VOIP network is, you can login using multiple devices at a time and answer/make call from any device. Even soft phone (software application) can be used. VOIP opens a whole new level of service compared to earlier technologies.

OSI Model

Quick ref table on each layers of OSI Model

✔ Application Layer

Protocol	Transport Port Number	Trasport Protocol used
HTTP	80	TCP/UDP
HTTPs	443	TCP/UDP/SCTP
POP	110	TCP/UDP
SMTP	25	TCP/UDP
FTP - Data	20	TCP/UDP
FTP - Control	21	TCP/UDP/SCTP
SSH	22	TCP/UDP/SCTP
Telnet	23	TCP/UDP
DNS	53	TCP/UDP
DHCP	67,68	TCP/UDP

✔ Presentation Layer 

Protocol	Transport Port Number	Trasport Protocol used
X.25	1998	TCP/UDP
Telnet	23	TCP/UDP
ICA
LPP

 

✔ Session Layer 

Protocol	Transport Port Number	Trasport Protocol used
SMPP	2775	TCP/UDP
RTCP	548	TCP/UDP
H.245		TCP/UDP
PPTP	1723	TCP/UDP
ZIP	1520	TCP/UDP
SDP		TCP/UDP
PAP		TCP/UDP

✔ Transport Layer 

Protocol	Important characteristic	PDU Name
TCP	Connection Oriented	Segment
UDP	Connetionless
SCTP	Connection Oriented
RUDP	Connection Oriented
UDP - Lite	Connetionless
Multipath TCP	Connection Oriented

 

✔ Network Layer 

Protocol	Important characteristic	PDU Name
ICMP	Error Reporting	Packet
IGMP	Multicast Group Membership Management
IPSEC	Secure IP network like VPN
RIP	Dynamic IP Routing, Hop count based routing. IGP
OSPF	Link state and link cost based routing
IPv4/IPv6	32 bit address, 128 bit address

✔ Data Link Layer 

Protocol	Services	PDU Name
HDLC	LLC - Logical Link Control Error control - ARQ, Flow control	Frame
LLDP	MAC - Medium Access Control CSMA/CD, LAN switching STP and SPB, MAC addressing, Store and forward, VLAN, QOS
Frame Relay	Encapsulation to frames
PPP	Frame sync
MPLS

✔ Physical Layer 

Technologies	PDU Name
OTN	Raw Bits
SDH
SONET