As from my understading, each Network will have their own PLMN with PLMN identity. This identity is read by the UE from SIB-1 message (plmn-IdentityList).
Question-1: Will this PLMN Identity vary from Cell to Cell or EnodeB to EnodeB of a Specific Network?
Question-2: Will this Tracking area code (in SIB-1 message) vary from Cell to Cell or EnodeB to EnodeB of a Specific Network?
No basically it should be same if you say it is a specific network.(home PLMN)
Answer 2: In any cellular network the tracking area is allocated to a group
of eNodebs. This is mainly done so that
the UE can easily be tracked and paged. If the mobile is at the border of a
tracking area then the Location area code can vary from e NodeB to eNodeB but
if the UE is not at the border of tracking area then it would not vary. (The
MME keeps track of the location of all UEs in its service area. When a UE makes
its first registration to the network, the MME will create an entry for the UE,
and signal the location to the HSS in the UE’s home network. The MME will then
keep tracking the UE’s location either via connection to eNodeB or at the level
of Tracking Area, which is a group of eNodeBs. MME is involved in every eNodeB change.
An idle UE will report its location either periodically, or when it moves to
another Tracking Area.)
Thats really useful information....
When a UE tries to attach to a network, UE will receive the attach acccept from netwok only if the Tracking area is not in the forbidden list. And Tracking area is identified by the Tracking area Indicator (TAI) which is constructed from MCC, MNC and Tracking area code (TAC).
What is the difference from the TAC and TAI?
I am giving a small example to differentiate TAC and TAI. Before that we have to know what is a PLMN id. PLMN id is super set of all id i,e TAC,Cell Id etc. That means every network operator in a region is identify by its PLMN. For example in Orissa we have three Network provide says Airtel, Realince and BSNL. Each Network operator has their own PLMN Id. Now PLMN Id consists of MCC and MNC. Mobile Country Code is same for a country and Mobile Network code varies with Operator and region. So Airtel, Realince and BSNL have the same MCC but the different MNC. So combination of MCC and MNC become a unique code in overall for all network and all region (inter country or intra country).
Now come to TAC. So As discuss in upper section a group of eNb is tagged as TAC. The same tracking area code may be present for other operator in a region. For Realince have tracking area code of 0x0001 the same TAC may for Airtel or BSNL. But adding to PLMN in TAC become a unique code.
So TAI = PLMN (MCC+MNC) + TAC
TAI = PLMN ID + TAC