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Ask the Expert: Demystifying Long-Term Evolution

Community Manager
Community Manager

With Rahul Pal, Arpit Menaria and Krishna Kishore 

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Welcome to this Cisco Support Community Ask the Expert conversation. This is an opportunity to learn and ask questions about evolution of long-term evolution (LTE) and the future with experts Rahul Pal, Krishna Kishore, and Arpit Menaria.

LTE, commonly marketed as 4G LTE, is a standard for wireless communication of high-speed data for mobile phones and data terminals. It is based on the GSM/EDGE and UMTS/HSPA network technologies, increasing the capacity and speed using a different radio interface together with core network improvements. The standard is developed by the 3rd Generation Partnership Project (3GPP).

Rahul Pal is a customer support engineer based in Bangalore, India. He has seven years of experience in the field of GPRS/UMTS/LTE technologies specializing in R&D and customer support. Rahul has worked with multiple vendors such as Nortel, NSN, and now Cisco, gaining expertise in packet core products such as SGSN and MME. Rahul has also worked as an escalation engineer handling customer escalations (technical troubleshooting and handling customer management). Rahul also has international experience of working directly with telco customers in the United States, Europe, and APAC and holds an engineering degree in information technology.

Krishna Kishore is currently working as a customer support engineer based in Bangalore, India, focusing on ASR5000/ASR5500, SAMI, and HWIC products providing support to 3G/4G mobility solutions deployed across the world. He has more than eight years of experience in mobility technologies such as GPRS/UMTS/LTE/CDMA, with experience in development and customer support. Krishna has worked with multiple vendor platforms such as Nortel, Hitachi, NSN, and Cisco. He holds a bachelor's degree in electrical and electronics engineering and CCNA certification. 

Arpit Menaria  is a customer support engineer based in Bangalore, India. He has been with the Cisco TAC for the past two and a half years (since July 2013) and has worked in FTS and TAC roles. Throughout his seven and half years of industry experience, he's worked for Ericsson and Tata Communications getting exposed to the telecom and Internet service provider environment. His technical skills span mobility, routing, switching, Linux, and Solaris. He has CCIE certification in routing and switching (written), RHCE, and WWSP mobility expert (written). Arpit also holds an engineering degree in electronics from the Indian Institute of Technology, Banaras Hindi University of Varanasi. 

Remember to use the rating system to let Rahul, Krishna and Arpit know if you have received an adequate response. 

Our experts might not be able to answer each question due to the volume expected during this event. Remember that you can continue the conversation in Wireless - Mobility,  sub-community Other Wireless - Mobility Subjects discussion forum shortly after the event. This event lasts through March 14, 2014. Visit this forum often to view responses to your questions and the questions of other community members.

11 Replies 11


Hello experts,

Please answer me something.  What are the key differences in architecture in LTE when compared to GPRS/UMTS technologies and what are key factors contributing towards high data rates in LTE?

Thank you.


Thanks for your Question Henry.

To start with LTE had undergone significant architectural changes during its evolution compared to GPRS/UMTS architecture.

Following is an architectural overview of LTE in terms on new nodes and interfaces added:


Key Differences in the architecture when compared to GPRS/UMTS

Radio/Access NW:

  • In case of GPRS/UMTS technologies, Radio side (GERAN) had the following nodes:

          2G services: BSC & BTS

          3G services: (UTRAN) consisted of RNCs & nodeB’s

  • In case of LTE the radio (Evolved UTRAN) made of collection of eNodeBs in the network.

Packet Core NW:

  • In case of LTE - MME, SGW, PGW & HSS were introduced which used to do functions of SGSN,GGSN & HLR in GPRS/UMTS technologies:

          MME: Looks after Control plane (signaling) functionalities (control plan anchor) in LTE.

          SGW: Looks after routing & forwarding of data packets in LTE.

          PGW: User Plan IP anchor point. Provides connectivity for the UE to external packet data networks.

          HSS: Acts as a centralized database that contains user related and subscription related info.

Regarding your Second Question on High Data Rates:

LTE technology has gone through several changes on the network which allows high data rate packet transfer.

The high data rates can be achieved because of the following factors:

  • Low data transfer latencies (sub-5 ms latency for small IP packets in optimal conditions) and lower connection setup time than with previous radio access technologies (GPRS/UMTS).
  • Simplification of radio architecture consisting of only eNodeB’s.
  • Use of OFDMA,MIMO, SC-FDMA access technologies.

Hi Guys,

It would be great if the working of LTE nodes(MME,SGW etc.) may be described in little more details with their name acronyms demistified.

How the Location update happens in LTE, is ther any change from GPRS/UMTS?

What are the Location Update, attach, PDP activation and detach equivalent call flows in LTE?

What are the interfaces with data charging nodes? what data charging nodes come in direct interfacing with LTE nodes?



Thanks for your question Akshay.

Below are the details about the LTE nodes -

MME is Mobility Management Entity and is in charge of all the Control plane functions related to subscriber and session management

    - For subscriber management it talks to the HSS (same as HLR in 2G/3G).

- It performs security procedures which relate to end-user authentication as well as initiation and negotiation of ciphering and integrity protection algorithm

- It also performs signalling procedures used to set up Packet Data context and negotiate associated parameters like the Quality of Service

- Apart from these, the MME also performs the task of idle terminal location management, I.e. The tracking area update (similar to RAU in 2G/3G) process used in order for the network to be able to connect to the UE in case of incoming sessions

SGW is Serving Gateway node

The SGW is responsible for communicating with the MME and PGW for doing the signalling for establishing a data-plane tunnel with the eNodeB and the PGW over which the subscriber data is sent.

From a functional perspective, the Serving GW is the termination point of the packet data interface towards E-UTRAN. When terminals move across eNodeB in E-UTRAN, the Serving GW serves as a local mobility anchor.

PGW is Packet Data Network Gateway

Similar to the Serving GW, the PDN gateway is the termination point of the packet data interface towards the Packet Data Network.

As an anchor point for sessions towards the external Packet Data Networks, the PDN GW also supports Policy Enforcement features (which apply operator-defined rules for resource allocation and usage) as well as packet filtering (like deep packet inspection for virus signature detection) and evolved charging support (like per URL charging).

From a functional perspective, PGW can be assumed quite similar to the GGSN used in 2G/3G technologies.

The tracking area is the LTE counterpart of the location area and routing area. A tracking area is a set of cells. Tracking areas can be grouped into lists of tracking areas (TA lists), which can be configured on the User Equipment (UE). Tracking area updates are performed periodically or when the UE moves to a tracking area that is not included in its TA list.

Operators can allocate different TA lists to different UEs. This can avoid signaling peaks in some conditions: for instance, the UEs of passengers of a train may not perform tracking area updates simultaneously.

The detailed call flows can be seen in 23.401 LTE 3GPP Spec reference document under below sections -

5.3 – Authentication, security and location management procedures    >>>> This will have all the attach, detach and location update call flows

5.4 – Session management procedures                                >>>> This will have all the default and dedicated bearer activation, QoS and interactions with PCRF etc.

5.5 – Handovers                                                     >>>> This will capture handover scenarios

Regarding your query on charging, please be informed the accounting functionality is provided by the Serving GW and the PDN GW which is similar to SGSN and GGSN in the older architectures.

The Serving GW shall be able to collect and report for each UE accounting information, i.e. the amount of data transmitted in uplink and downlink direction categorised with the QCI and ARP pair per UE per PDN connection.

Please let me know this answers your question.

Also, if you can be more specific in your query, probably I will be able to provide you the exact answer.