Inside SSE Trading Units (PBU) and Connected Circles: From Trading Seats to Institutional Trading Infrastructure#
When investors look at the stock market, they usually see:
Stock price
↓
Order submitted
↓
Trade executedHowever, the real exchange infrastructure underneath is much more complicated.
A real institutional order travels through:
Investor Account
↓
Brokerage Trading System
↓
Order Management System (OMS)
↓
Trading Unit (PBU)
↓
Exchange Gateway
↓
Matching Engine
↓
Clearing and Settlement SystemThe hidden infrastructure connecting market participants to the exchange is:
- Trading Seat
- Trading Unit
- PBU (Participant Business Unit)
- Connected Circle
These concepts define how securities firms, funds, insurance companies, and quantitative firms actually access the Shanghai Stock Exchange (SSE).
1. From Trading Floors to Digital Trading Units#
The era of physical trading seats#
In the early days of China’s securities market, exchanges operated with a traditional membership and seat model.
A seat was literally a physical position inside the trading hall.
A securities firm would send representatives, often known as “red vests”, to the exchange floor.
The workflow looked like:
Investor
↓
Broker Branch
↓
Telephone
↓
Trading Representative
↓
Exchange Seat
↓
Exchange SystemAt that time, a seat represented:
- Exchange membership;
- Trading rights;
- Physical access point;
- Communication channel.
The seat was both a legal right and a technical entry point.
2. Why Did Seats Evolve into PBUs?#
As China’s securities market expanded, one seat could no longer support modern institutional requirements.
A large securities firm might operate:
- Retail brokerage;
- Proprietary trading;
- Asset management;
- Margin financing;
- Institutional execution;
- Quantitative trading.
If all businesses shared one seat:
Brokerage
+
Proprietary Trading
+
Asset Managementthere would be serious problems:
- Poor risk isolation;
- Difficult compliance management;
- Lack of business-level control.
Therefore, exchanges separated:
membership rights
from
transaction execution identity.
This created the concept of:
Trading Unit / PBU#
3. What Is a PBU?#
PBU stands for:
Participant Business Unit
A PBU is a logical trading identity recognized by the exchange.
It is not simply a network connection.
It represents:
- Who is submitting orders;
- Which business line owns the order flow;
- Which permissions apply;
- Which risk controls are triggered.
A securities company may have:
ABC Securities
├── PBU001 Proprietary Trading
├── PBU002 Asset Management
├── PBU003 Brokerage Business
└── PBU004 Quantitative TradingWhen the exchange receives an order, it does not simply see:
“Investor Zhang buys 10,000 shares.”
Instead, it sees:
Securities Account
+
Trading Account
+
PBU Identity
+
Order InstructionThe PBU becomes the exchange-side identity of the transaction.
4. The Three-Layer Structure: Seat, PBU, Connected Circle#
Modern exchange infrastructure can be understood through three layers.
Layer 1: Seat#
Purpose:#
“Who has the right to participate?”
The seat represents:
- Membership;
- Exchange rights;
- Legal qualification.
The seat is mainly a membership concept.
Layer 2: PBU Trading Unit#
Purpose:#
“How does an institution actually trade?”
The PBU provides:
- Trading identity;
- Permission control;
- Risk management boundary;
- Exchange connectivity.
Actual order submission happens through the PBU.
Layer 3: Connected Circle#
Purpose:#
“How can multiple PBUs be managed together?”
Several PBUs can be grouped into a:
Trading Unit Connected Circle
Example:
Main PBU
|
--------------------------------
| | |
PBU-A PBU-B PBU-CThe connected circle provides a logical organization layer above individual PBUs.
5. What Is an SSE Connected Circle?#
A connected circle is a group of related trading units managed together.
It is designed for institutions that have:
- Multiple products;
- Multiple strategies;
- Multiple trading accounts;
- Multiple execution channels.
For example:
A fund company may have:
Fund A Trading PBU
Fund B Trading PBU
ETF Trading PBU
Private Fund Trading PBUThese may be organized into different connected circles depending on operational requirements.
6. Connected Circle and Front-End Risk Control#
One of the most important functions of the connected circle is:
exchange-level risk control.
Large institutions can create enormous buying pressure.
The exchange therefore needs a mechanism to prevent:
- Excessive intraday buying;
- Settlement risk;
- Operational mistakes.
The SSE applies front-end control based on:
Net Buy Order Amount During The DayA simplified calculation:
Buy Order Amount
-
Sell Execution Amount
-
Cancelled Buy Orders
-
Price Difference AdjustmentsWhen the limit is reached:
The exchange rejects:
New Buy Ordersbut still allows:
Sell Orders
Cancel RequestsThis works as an exchange-level safety firewall.
7. How Connected Circle Limits Work#
Assume:
Connected Circle A
Main PBU
|
-----------------
PBU-1
PBU-2
PBU-3The circle has:
100 billion RMB trading limitDuring the day:
PBU-1 buys 40 billion
PBU-2 buys 30 billion
PBU-3 buys 20 billionThe system calculates:
90 billion usedOnly:
10 billion remainingis available.
A new 20 billion buy order will be rejected.
The control happens at the connected-circle level, not only at the individual PBU level.
8. How Brokerage Systems Map Orders to PBUs#
A real brokerage architecture looks like:
Mobile App
↓
Customer Gateway
↓
Brokerage Core System
↓
OMS
↓
Order Routing Engine
↓
PBU Mapping
↓
Exchange Gateway
↓
SSE Matching EngineBefore an order reaches the exchange, the brokerage system determines:
- Which trading account;
- Which product;
- Which PBU;
- Which permissions;
- Which risk limits.
9. Why Fund Companies Care About PBUs#
Investment funds usually do not directly connect to exchanges.
Instead, they lease trading units from securities firms.
A fund company may operate:
PBU001 Equity Funds
PBU002 Bond Funds
PBU003 ETF Business
PBU004 Private MandatesAdvantages:
Business isolation#
Different strategies remain separated.
Unified risk management#
Multiple products can share controlled limits.
Operational efficiency#
The institution can manage many products through structured trading identities.
10. Why Quantitative Firms Need Dedicated PBUs#
Quantitative trading is extremely sensitive to infrastructure.
A high-frequency strategy may generate:
Millions of orders per dayThe important resources include:
Order throughput#
How many messages can be sent per second.
Independent execution path#
Avoiding congestion with other clients.
Dedicated risk configuration#
Different strategies require different controls.
Many “VIP trading channels” in the market are essentially combinations of:
- Dedicated PBU;
- Dedicated network connection;
- Dedicated execution resources.
They do not change exchange matching rules.
They reduce resource contention.
11. The Relationship Between PBU and Market Data Like龙虎榜#
Investors often see:
Top Buying Brokerage
Top Selling Brokeragefrom public trading reports.
However:
A brokerage seat does not equal one investor.
Behind one displayed broker location may exist:
- Many customers;
- Multiple accounts;
- Different strategies;
- Multiple PBUs.
Therefore:
Public trading data shows market behavior.
It does not directly reveal the underlying connected circles.
12. Shenzhen Exchange and PBU Architecture#
The Shenzhen Stock Exchange uses a similar concept:
Member
↓
Trading Unit
↓
Exchange Trading SystemThe underlying philosophy is the same:
Separate:
- Membership rights;
- Trading identity;
- Business organization.
The differences mainly come from historical evolution and detailed rule implementation.
13. Evolution of China’s Securities Trading Infrastructure#
The evolution can be summarized as:
Stage 1: Manual Trading#
Trading Floor
↓
Human Representatives
↓
Telephone OrdersStage 2: Electronic Seats#
Broker Branch
↓
Trading Terminal
↓
Exchange HostStage 3: PBU Era#
Member
↓
Trading Unit
↓
Exchange SystemStage 4: Connected Circle Era#
Multiple PBUs
↓
Business Organization
↓
Risk Control
↓
Institutional Trading14. Why PBU Is the Hidden Nervous System of the Market#
Different participants see different layers.
Investors see:
AccountBrokerages see:
CustomerExchanges see:
PBURegulators see:
Trading BehaviorThe PBU connects:
Account Management
+
Trading Permission
+
Risk Control
+
Clearing Path
+
Execution InfrastructureConclusion#
The SSE PBU Connected Circle system is not just a technical configuration.
It is a core component of China’s securities market infrastructure.
Its evolution reflects the transformation:
Physical Trading Seat
↓
Electronic Seat
↓
Trading Unit PBU
↓
Connected Circle NetworkToday, billions of dollars of institutional capital move through a hidden infrastructure built from:
Trading Units
PBUs
Connected Circles
Exchange GatewaysThe price chart is visible.
The infrastructure that makes the market function is not.
Behind every order, there is a PBU.